How can I deal with extreme temperatures in a hotel room?

It seems contradictory, but keeping the windows (and shades/shutters) closed during the day really help prevent too much heat accumulation. It works best if you can close them while the morning is still cool. Then as soon as the evening is cooler than your room, opening the windows allows the heat to escape more optimally. When I moved to the South of France my neighbors used to laugh at me throwing the windows wide open when the forecast was high - they were right, when I learned to close the shutters instead I did much better. Most hotel windows in Germany should be equipped with shades/curtains and possibly shutters.

I also like the suggestion to ask the reception for a fan. If you are in the same hotel for a significant amount of time, like a week, it might even be worthwhile for you to just buy a fan at a local hardware store. Smallish expenditure, much increase in comfort.

If the bed has duvet, then take the duvet out of its cover. Then use the duvet cover as a light blanket/sheet. This will provide minimal insulation, and make the bed feel cooler.

You can acclimatise to heat. After all, humans evolved in a warm climate. According to the University of Connecticut, it takes one or two weeks:

Heat acclimation is a broad term that can be loosely defined as a complex series of changes or adaptations that occur in response to heat stress in a controlled environment over the course of 7 to 14 days. These adaptations are beneficial to exercise in the heat and allow the body to better cope with heat stress. Heat acclimatization describes the same process, but happens in a natural environment. In either case, the positive adaptations that occur include reductions in:

• Heart rate
• Body temperature responses
• Skin temperature responses
• Perceived exertion

So the solution is: adapt and get used to the heat. Rest a lot and stay hydrated. Don't over-exert yourself, in particularly not during the first days. It probably helps to not spend much time in an artificially cooled environment; from personal experience in the USA, where air-conditioning is present and often much colder than I find comfortable or healthy (I've caught colds), I've found that air conditioning hinders the heat acclimatisation.

A hot shower will cool you off more than a cold shower. Hot water will increase blood flow to the skin, which will make your evaporative cooling work better.

Reference https://theconversation.com/health-check-do-cold-showers-cool-you-down-71004

The verdict Our bodies respond more to changes in skin temperature than core temperature. So, if we cool part of the body (for instance with a cold sponge, or cold shower), skin blood flow decreases and skin temperature falls.

Here we “feel” cooler because cold water causes cold temperature receptor activation in the skin. We may also feel more comfortable, as our skin temperature enters the comfort zone. But because there is less blood flowing to the skin, we’ll actually keep more heat inside, thus leading to an unintended overall increase in core temperature.

A cold shower to “cool off” might seem a good immediate choice. We feel cooler because of the combination of the cold water and the decreased blood flow to the skin, but in fact our core will get warmer because of reduced heat loss from the body without skin blood flow. Some minutes later, we feel hot again. But a warm sensation on the skin will lead to increased blood flow to the skin, increasing heat loss from the body.

So, keeping cool in summer will be more effective with a warm shower (water temperature about 33?C) rather than a cold shower (water temperature 20-25?C). It will seem warm initially but after a few minutes will provide better comfort in the long term.

I've realized that this seems only common practice in Southern Europe (Portuguese here), due to the other answers, but the first thing I've learned to do during the summer while growing up is to always have the shutters down and the window(s) open.

Especially if where you're staying is directly facing the sun, because this avoids the heat coming in but still allows the air to flow.

Adding to this, taking the cold showers (like you did), drinking fresh fluids (water is ideal) and having wet towels (with cold water, obviously) around to keep your body refreshed. If you wanna use clothing, make sure to use "breathable" clothing and light colours.

You can acquire a small portable fan for not very much money at all (£10 for a reasonable one) and they are surprisingly powerful. Get one that can be plugged in and you can bring it with you and leave it running at night to give yourself some airflow.

The other answers offer some tips with dealing with the heat, but they'll only take you that far. Cold rooms are easy to deal with by using your jacket or asking for an extra quilt. But a hot room is simply intolerable for most.

So although in the OP you ask what to do if there is no air-conditioning, the real answer is to never get into that situation again. Most hotel-booking websites allow for filters in your search, so use them. Never again book a room with no A/C if the weather forecast is above your comfort zone.

The only solution that actually works is getting some sort of AC, or other active cooling to lower-than-ambient temperature, of your own. Evaporative cooling is useless in most climates; it just adds humidity that makes the heat more unbearable. Compressor-based AC is going to be bulky and hard to travel with. Some less conventional options that remain are:

• Thermo-electric cooling (peltiers). It's going to be hard to effectively move heat outside or get enough to make the room climate bearable, but they're tiny and dirt cheap and you can literally strap them to your body, then just move the high temps off the hot side with a room fan. It won't make the room comfortable but it will keep you cool.

• Dry ice, if you can get it where you are, will absorb a lot of heat as it sublimes, and make any surface it's in contact with sufficiently cold to rapidly condense moisture out of the air, fixing the humidity problem that's probably the main reason the heat is so unbearable. In the US it's easy to get for $2/lb at grocery stores. Not sure about elsewhere.

• Plain ice. Lots of it. With fans blowing over it. If you can put a large smooth surface against it you can probably condense water out of the air too to lower the humidity, but a good deal of it will evaporate as well as it melts.

In either of these options, keeping the condensed or melted water in sealed containers (so it can't evaporate back into the room air) can absorb more heat; once it reaches equilibrium you can pour it out. Or you can drink it while it's still cold to cool down.

To answer the question about what to do in a room that's too cold, a hot water bottle can help a lot. Even if you haven't planned in advance and brought one with you, they are relatively inexpensive. If your room has hot drink making facilities you can use those to fill it with properly hot water, but if not then even just the hot water from the tap will make it warm. If the hot water bottle doesn't have a cover, and you want to fill it with hot rather than warm water, you can wrap it in a towel.

You can take the hot water bottle to bed with you. Depending on personal preference, and how cold the room is, you may want to cuddle it or otherwise have some part of your body in contact with it (provided it is either filled with water that is not very hot or else is securely wrapped in a cover or towel!), or just have it under the blankets with you at some distance from your body. You can also place the bottle in the bed a few minutes before you get in yourself, so that it warms the place where your body will be.

You can also use it while you're still up. You can place it on your lap or under your feet (having removed shoes) so that your hands are free. (Again, make sure that either the water inside is not too hot, or it is wrapped up in an insulating covering!)

Building on @BKlassen's answer, you can purchase cooling towels that will make a difference, but only if the humidity isn't so high that evaporative cooling can occur.

When we travel to SE Asia, we bring them with us. You soak the towel in water and drape it over your neck so it touches the skin by your carotid arteries. While not super effective in high humidity, they still work, just not as well as they do in lower humidity.

I don't know how readily available they may be in Germany, but they're easy to find in the US. Google "cooling towel" and you'll find many examples. Failing finding them available, a microfiber towel will do quite well. You can find them at auto parts stores, department stores, etc. You may have to read labels to find out what the towels are made of. Some of our towels are labeled "viscose" and that type of fabric will work well too. We keep a couple of those on our boat.

Another thought I had, can your hotel move you to a room on a lower floor? Heat rises, and if you're basically in the attic, you're the recipient of all the heat rising inside the building.

According to this question on history SE about how ancient desert civilizations stayed cool allowing water to evaporate can help a lot with cooling.

Answers to this question mention wrapping oneself in a damp blanket that will draw the heat from you as the dampness evaporates. Answers also mention filling water pots around the room which may be applicable if cookware pots are available in the room.

Other answers are likely not applicable once a hotel has been selected as they relate to building construction.

If having extra items with you is not a problem (e.g. you travel with the car), you could bring your own small fan or a portable A/C unit with you. There are A/C units which cool air by evaporating water from a reservoir: those won't cool an entire house, but perform better than a simple fan, and can be quite small (some are USB-powered). Compressor-based portable A/C units also exist, though it may be a challenge to find one which is reasonably small to bring along.

Speaking of water evaporation, you don't have to take a cold shower to cool off: any shower will moist your skin which will keep releasing that water for some time. Trying to cool off quickly with a cold shower can make you catch a cold, and the effect of cold water is pretty much over by the time you're out of the bathroom.